Rare UK species need habitat conservation
26 February 2009
New research published in Proceedings of the Royal Society B has revealed the importance of habitat conservation in helping threatened species survive environmental change.
Silver spotted skipper.
Researchers from Exeter, Sheffield and York Universities used a computer model to simulate the recovery of a rare species of British butterfly during the 1980s and 1990s. The results of this study could inform future conservation policy and protect vulnerable species against the effects of climate change and habitat destruction.
Effective conservation management is essential to promoting the survival and recovery of Britain's rare species. In lowland Britain, urbanisation and intensive agricultural practices have severely reduced the availability of suitable habitats and many animal populations are now isolated and susceptible to future environmental change.
The study, funded by the Natural Environment Research Council, concentrates on understanding the recent expansion of a rare butterfly species confined to the chalk grasslands of southern England, called the silver-spotted skipper.
'Our main result is that habitat fragmentation by human activities - the fact that habitat is now restricted to much smaller and isolated areas - is a significant constraint on whether a species expands it's distribution in the modern landscape', says Dr Robert Wilson from the University of Exeter and lead author of the study.
Using relatively simple information about butterfly populations and suitable habitat locations, the team are able to predict which landscapes would have the best chance of producing a recovery in butterfly population.
Dr Wilson explains, 'This should be able to help us in terms of prioritising which landscapes we carry out conservation management in, or even what kinds of conservation management we carry out.'
The silver-spotted skipper lays it's eggs on Sheep's Fescue Grass in the chalk grasslands of southern England. During the 20th Century, more than three quarters of such habitats were destroyed as a result of changes in farming practice. By 1982, there were fewer than 70 populations of the silver-spotted skipper, almost all in five networks of chalk hills in Sussex, Kent, Hampshire, Surrey and the Chilterns, covering a total area of only a few square kilometres.
Through the 1980s and 1990s, reintroduction of grazing livestock by environmental stewardship programmes, and climate warming that allowed butterflies to lay eggs on the colder northern slopes of grassland hills, led to a recovery in the butterfly population. By 2000, butterfly populations covered more than ten times the area recorded in 1982.
The researchers used a computer model to reproduce this recovery in silver-spotted skipper populations. The results show that despite some growth of butterfly populations, further population expansion was hampered by the sparse distribution of suitable habitats and no butterfly population was able to spread further than thirty kilometres from it's original position.
Enabling butterfly populations to spread by linking fragmented habitats is vital to genuine population recovery. If butterfly populations remain isolated, they are more vulnerable to extinction by local environmental changes such as anomalous seasonal weather. Computer models similar to those used in this study could therefore be used by conservation organisations to make predictions of butterfly expansion in response to landscape changes, and maximise the butterfly recovery achieved using limited resources.
Findings apply to other rare species
The findings of this study can also be extended to many other rare species living in fragmented specialist habitats - for example insects, birds and small mammals found in grasslands and woodlands.
An advantage of this method is that the computer model used for making predictions requires only simple information about rare species numbers and the location and quality of suitable habitats. The information used in this study was collected by looking for butterflies across all the chalk grasslands of southern England in both 1982 and 2000.
'The silver-spotted skipper is very recognisable - a small, orange butterfly which darts low over the ground, and perches on areas of bare ground and low-growing flowers. When the butterfly closes its wings it has an unmistakable pattern of silver spots on a greenish background', recalls Dr Wilson.
'Sites where butterflies weren't found were revisited to search for eggs. This involved walking stooped over the hillside, searching for Sheep's Fescue plants and the unmistakable white, pudding-bowl shaped eggs of the butterfly,' he added.
The results also show that habitat conservation is vital for rare species to survive climate change. With the Intergovernmental Panel on Climate Change predicting a 2-4oC rise in mean annual temperature over the coming century, large changes in species distributions are expected as species move north towards the cooler latitudes. So, conserving specialist habitats at the northerly range of rare species is important because these are the populations that need to survive and expand in response to climate change.
The silver-spotted skipper, also found in southern Europe, is now suffering extinction in the warming foothills of central Spain.
The type of modelling approach used successfully in this study will focus conservation efforts trying to help rare species widen their geographical ranges and adapt to global warming.
Modelling the effect of habitat fragmentation on range expansion in a butterfly, Proceedings of the Royal Society B.
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